When click-dragging an image to the desktop activity and clicking to set as wallpaper from a remote location (WebDAV and a HTTP file on a website were tested) doesn't set the wallpaper to the correct image but turns the background black. Right-clicking/clicking the toolbox and clicking, "Desktop Settings" shows in the wallpaper picker a wallpaper with a name matching the filename of the remote image, but it simply says, "0x0" underneath it and has no preview available. Setting the desktop background to one of these wallpapers results in the same black background described above.
Just tested it (webdav at least, from my owncloud), and it works flawless for me (4.8.3). Looks like the file is not being downloaded/is corrupt... Can you do other things with it? Drag it to Dolphin and view it, or so?
Could you please specify the version of KDE in the box above?
I can view the image in any program, navigate to the parent folder in Dolphin and download it either via Dolphin/KIO or from KGet. I don't get this problem with local files - I am able to manually download them, then click-drag them to the desktop and successfully set as wallpaper.
Added version number information - I'm currently running SC 4.8.3.
Still appears to be present in KDE 4.10.5 when using HTTP URLs.
It happens to me with my Laptop. When I try to put a image like wallpaper dragging and dropping from a web browser (firefox or rekonq) appears the options for the widgtes and for the wallpaper. If i select "use image as wallpaper", the wallpaper turns in black.
KDE Application 4.14.2 in LinuxMint 17.1
This bug report was filed for KDE Plasma 4, which reached end-of-support status in August 2015. KDE Plasma 5's desktop shell has been almost completely rewritten for better performance and usability, so it is likely that this bug has already been resolved in Plasma 5.
Accordingly, we hope you understand why we must close this bug report. If the issue described here is still present in KDE Plasma 5.12 or later, please feel free to open a new ticket in the "plasmashell" product after reading https://community.kde.org/Get_Involved/Bug_Reporting
If you would like to get involved in KDE's bug triaging effort so that future mass bug closes like this are less likely, please read https://community.kde.org/Get_Involved#Bug_Triaging
Thanks for your understanding!